Tank for storing cryogenic fluids and mehtod for constructing a fluid tight tank

ABSTRACT

The invention relates to a tank ( 11 ) for storage of cryogenic fluids. The tank ( 11 ) comprises a base section ( 12 ), a vertical wall element ( 14 ) and preferably an upper top ( 19 ). The tank ( 11 ) is provided with a fluid tight barrier ( 26 ) intended to prevent the stored fluids to escape to the surroundings. The fluid tight barrier ( 26 ) is formed of thin metal plates joined together. At least the vertical wall ( 14 ) comprises an inner structurally supporting wall element ( 24 ) and an outer structurally supporting wall element ( 25 ). The fluid tight barrier ( 26 ) is arranged between the inner ( 24 ) and the outer ( 25 ) structurally supporting wall element. The invention relates also to a method for constructing such tank ( 11 ), where the base part ( 12 ) is firstly erected whereupon a vertical wall ( 14 ) is concreted, preferably by means of slipforming or jumpforming. Firstly, the inner structurally supporting wall element ( 24 ) of the wall ( 14 ) is reinforced and concreted, whereupon a fluid tight barrier ( 26 ) is arranged on the external side of the inner structurally supporting wall element ( 24 ), whereupon the outer structurally supporting wall element ( 25 ) is reinforced and concreted.

The present invention relates to a tank for fluid storage. Further thepresent invention relates to a method for building such tanks for fluidstorage.

The invention relates preferably to a free-standing tank comprising abase part, a vertical wall and preferably an upper top. It should beemphasized that the fluid may also be a gas of any type or a liquid ofany type. The stored products may be fluid products on a hydrocarbonbasis or contaminating fluids of a type which should not be allowed togo astray. The stored fluid may also be cryogenic.

It has previously been known to use concrete tanks for storage ofcryogenic fluids. Such tanks consist generally of an inner fluid tighttank surrounded by a concentrically arranged outer tank. The inner tankis supported by a support structure resting on the bottom of said outer,concentrically arranged tank. Insulation materials are arranged in theintermediate space between the inner and the outer tank. Due to itscapillary proper-ties, concrete as a material is not necessarilycompletely tight. Further, small cracks may often appear in theconcrete, either as a result of the curing process in the concretingphase or as a result of loads acting on the concrete. Hence, there is aneed for securing a fluid tight wall in a different manner. It haspreviously been proposed to cover the inner wall of such tanks with amembrane formed by thin, steel plates joined together.

NO Patent Specification No. 310.699 describes a storage tank forcryogenic liquids, in particular liquefied gasses such as LNG. Thestorage tank comprises an inner tank and an outer tank where at leastthe inner tank is made of concrete. Heat insulation materials are placedbetween the side walls and bottom structure of the tank. The inner tankconsists of gas tight concrete, in which prestressing cables forprestressing of the tank are installed. The cables are to beposttensioned subsequent to cooling of the tank. Further, at theexterior surface of the inner tank a liner is arranged in order tocollect possible leaked liquid from the interior of the tank. Suchsolution requires further a pipe system for circulation of gas,installed between the liner and the exterior of the inner tank, in ordergas to monitor possible leakage. Further, a pipe system for circulationof a coolant is arranged in the wall of the inner tank, whereby the tankwall can be cooled down prior to filling of LNG into the tank.

Norwegian Patent Specification No. 142.144 discloses a tank for storageof highly pollutant liquids. The tank comprises an inner tank and anouter tank of concrete. Insulation materials are placed between theinner and the outer tank wall. The wall of the outer tank is made ofprestressed concrete and is further fixed to the base plate of the tank.The inner tank is made of an inner thin walled barrier in the form ofthin steel plates—two elastic layers intended to compensate for possiblecontraction or expansion caused by temperature variances appearing whenfilling of LNG. A layer of insulation is further placed between theinner tank and the outer tank wall. In addition, the inner tank has abase plate formed of plates. The inner fluid tight barrier and theplates forming the base plate are made of an aluminium alloy. The innerwall is made as a non-selfsupporting thin wall structure, supported bythe insulation layer, placed between the inner and the outer tank walls.A thin liquid barrier is installed on the interior side of the outerconcrete wall.

GB Patent Specification No. 1.341.892 shows a storage tank for cryogenicliquids. The tank is provided with an inner concrete wall and a liquidtight steel membrane arrange outside of the concrete wall. A layer ofinsulation materials is placed outside the steel membrane. The exteriorof the tank is covered by steel plates.

US Patent Specification No. 4.366.654 shows a tank for storage ofcryogenic fluid, consisting of an inner liquid tight tank of steel inthe form of a layer of steel plates, a surrounding concrete wall havingan L-shape and a layer of insulation materials arranged between theconcrete wall and an externally arranged, outer wall. Inside the outerconcrete wall, facing the layer of insulation materials, an insulationliner provided with an inner layer of insulation materials in the formof polyurethane foam, is arranged.

For such prior art solutions, in which the inner tank wall is made ofthin plates, the thin plated part of the wall will contract heavily dueto the drop in temperature during filling of LNG into the tank. Aresult, the thin wall will contract more than the insulation arrangedoutside of the thin wall. Consequently, the support of this part of thewall will be reduced and in extreme cases will be non-existent. Inparticular, the transition zone between the inner base plate and theinner wall will be a weak point. This may also cause cracking of theinner wall.

A further drawback with the prior art solutions is that the liquid tightthin inner wall also may be damaged, for example when exposed to forcesfrom earthquakes, external loads, impact or the like.

A further drawback may be the cost level for construction, in particularsince rigid requirements both to tightness and safety have to be met.

The object of the present invention is to provide a tank solutioneliminating most of the drawbacks of the prior art solutions and at thesame time achieving a cost and construction effective solution. Afurther object is to provide a solution which eliminates, or at leastreduces, the possibilities of cracking of the liquid tight wall and/orexposure of the outer wall.

The objects are achieved inter alia by providing a wall, base plate andtop structure as further defined in the claims and in particular inclaim 1.

Further the objects are achieved by means of a method as further definedin the method claims.

From a principle point of view the inner wall element and the outer wallelement of the inner wall is designed to take the forces acting on thewall, while the intermediate wall element forms a fluid tight barrierwithout substantial load carrying capacities.

When filling a cryogenic liquid into the tank the fluid tight wallelement, which preferably is made of thin sheets of Ni-steel, tends tocontract more than the inner concrete wall element. Hence, the innerwall element functions as a restraint for the fluid tight wall elementwhile the fluid tight wall element exerts a prestressing force onto theinner wall element when the tank is filled with a cryogenic liquid.Further, both the inner wall element and the outer wall element functionas a protection for the intermediate fluid tight wall element. The outerwall element will protect both the fluid tight wall element and theinner wall element for externally imposed forces and will in additiontake pressure forces imposed by the content of the tank.

It should be noted that the tank also is suited for different othertypes of storages, such as storage of fluid exposed to a limitedpressure, storage of environ-mental detrimental fluid, or storage offluids having a high temperature.

Essential characteristics for the solution according to the presentinvention may be:

-   -   optimum use of materials    -   minimum use of expensive materials    -   effective exploitation of the strength of cheap materials.

A preferred embodiment of the present invention will be described indetail below, referring to the Figures wherein:

FIG. 1 shows a simplified vertical section through a tank according tothe present invention, used for storage of cryogenic fluids;

FIG. 2 shows a simplified horizontal section through the tank shown inFIG. 1, seen along the line 1-1;

FIG. 3 shows in detail a detail A, indicated in FIG. 1;

FIG. 4 shows a way of welding two adjacent edges of adjacent steelplates, for formation of a fluid tight barrier; and

FIG. 5 shows a preferred method for welding together the edges onadjacent steel plates.

FIG. 1 shows a freestanding, cylindrical tank 10, comprising an inner,fluid tight tank 11. The inner fluid tight tank 11 comprises a baseplate 12 resting on a support 13. Further, the tank 11 comprises avertical wall made of prestressed concrete and an upper top 15.

Further, the tank comprises a concentric, outer tank 16 made ofprestressed concrete. The outer, concentric tank comprises a base plate17 founded on a layer of gravel on the ground. The base plate is made ofprestressed concrete. The tank 17 comprises a cylindrical concrete wall18 extending vertically upwards, supporting a dome shaped roof 19.

The concrete plate 17, the upper dome 19 and the walls 14, 18 in theinner and outer tank are reinforced, preferably prestressed.

Insulation materials 20 of any suitable type are arranged in theintermediate space between the inner tank 11 and the outer, concentrictank 16. Such insulation material may be pearlite.

The support 13 for the inner tank 11 may preferably be formed by acircumferentially arranged base 21 made of wood, the verticalcylindrical wall 14 being directly supported by the circumferentiallyarranged base 21. The base plate 12 of the tank 14 may for example bemade of plywood and may for example have a thickness of 200 mm. The baseplate 14 may be supported by a number of parallelly arranged beams 22,e.g. 2000 mm×1000 mm. Centre to centre distance for the beams 22 may forinstant be 12000 mm.

On the upper side of the base plate 12 a fluid tight barrier 23 isarranged. According to the embodiment shown in FIG. 1 the fluid tightbarrier 23 is made of thin steel plates having a thickness of 4 mm.

As indicated in FIG. 1 and further shown in FIG. 3 the inner, verticalwall 14 comprises an outer 25 and inner 24 structurally supporting wallelement and an intermediate fluid tight barrier 26. The intermediatefluid tight barrier 26 is joined with the fluid tight barrier 23 restingon the tank base plate 12. Said joint is also made fluid tight.

The fluid tight barrier 26 may for example be made of thin plates joinedtogether along the plate edges to form a fluid tight joint. The jointmay be made in any suit-able, conventional manner. The edges of themetal plates may for example be bent up and the upper end of the edgesof the metal plates may then be bent and folded together. Alternativelyand/or in addition the edges may be welded together. Dependent upon thechoice of material the plates may optionally be glued together. In thelatter case it may suffice to let the plates partly overlap and thenapply glue.

FIG. 3 shows in detail a section at the lower end of the wall 14 in theinner tank 11. The vertical wall 14 rests on a ring formed beam 21,preferably made of wood. At its lower end the vertical wall 14 isprovided with a horizontal metal plate, preferably steel. The steelplate extends into the inner tank 11 and is via an expansion loop 30connected fluid tight to the fluid tight barrier 23, resting on the tankbase plate 12. As specified above the vertical wall 14 comprises aninner structurally supporting wall element 24 and an outer structurallysupporting element 25. A vertical fluid tight barrier 26, fluid tightlyjoined with the plate 27 forming the lower end of the vertical wall 14,is arranged between said wall elements as an integral part of thevertical wall 14. In order to secure adequate transfer of forces fromthe base plate 12 to the vertical wall 14, for example caused bycontraction of the tank due to cooling the content down to cryogenictemperatures, vertical ring shaped plates 28, 29 made of metal arewelded to the lower plate 27. At least at their upper end of the plates28, 29, securing embedment means 31 are arranged in order to securetransfer of loads and forces into the concrete wall. Said embedmentmeans 31 may preferably be arranged at different vertical levels.

Ductility and fluid tightness are the most important properties of theintermediate fluid tight barrier 26. In particular ductility is veryimportant if the fluid to be stored is cryogenic. The fluid tightbarrier 23, 26 should be made of a material which may withstand thefluid to be stored. The types of material may for example be metalplates, for instant made of Ni-steel, plastic materials in the form offilms, membranes in the form of epoxy, etc.

FIG. 4 shows a preferred way of establishing a fluid tight joint betweentwo adjacent steel plates. The side edges are bent upwards and weldedtogether at two different levels by means of a continuous, fluid tightwelding seam 32.

Correspondingly the outer tank comprises a base plate and verticalwalls. At its upper end the tank is equipped with a roof structure, forexample in the form of a dome or a truncated cone.

The function of the inner structurally supporting wall element 24 is toprotect the membrane from loads and impacts from the stored fluid andalso to form support for the membrane, in particular when the fluid iscooled down to cryogenic temperatures. The outer structural part 24shall in particular take up loads and forces and should consequently beprestressed. The wall should in addition preferably be ordinary,non-prestressed, reinforced.

Dependent upon the fluid to be stored, the membrane or the intermediatefluid tight barrier 26 may be formed of plastic materials, such asplastic sheets or a layer of epoxy.

The outer tank 16 may also be equipped with a vapour barrier of a thinplated material. The vapour barrier may be arranged and fixed on theinterior wall of the outer tank 16 in any known manner. In analternative embodiment the wall of the outer tank 16 may be constructedmore or less in the same manner as the wall of the inner tank 11,thereby providing a inner layer of concrete, surrounded by a thin platedfluid tight barrier, applying the same principles as described above.The outer layer is then concreted and prestressed. It would bepreferable if the concreting of the inner tank wall and the outer tankwall are performed in the same slipforming operation, although atsufficient different levels to enable mounting the intermediate metalplates.

A preferred method of construction of a fluid tight tank of prestressedconcrete for storage of fluids, preferably cryogenic fluids, will bedescribed below. According to such embodiment the tank comprises in anycase an inner fluid tight tank made of prestressed concrete, for exampleas described above. The inner tank comprises a base, a vertical wall ofconcrete and preferably an upper top.

Firstly, a footing is constructed whereupon the foundation of the tankis constructed. A vertical wall structure 24 is then concreted,preferably by means of slipforming or jumpforming. The first stage inthis process is to erect the formwork for the inner structurallysupporting element on said foundation, whereupon an inner structurallysupporting element 24 is reinforced and concreted. Then the fluid tightbarrier 26, arranged on the exterior of said inner structurallysupporting element 24 is installed whereupon the outer structurallysupporting element 25 is reinforced and concreted.

The lower part of the wall is erected on a foundation, the lower part ofwhich comprises a base plate 27 of steel, an inner and outer steel plate28, 29 extending along the inner and outer circumference of the wall andfixed by means of welding with the horizontal base plate 27. Further,the lower end of the intermediate thin plated fluid tight membrane 26 inthe form of steel plates are fixed by welding to said horizontal baseplate whereupon this part of the wall is reinforced an concreted.

Preferably, both the inner and the outer structural supporting wallelements 24, 25 are concreted by means of slipforming or jumpforming.

According to an embodiment the inner structurally supporting wallelement 24 is concreted at least partly up to a level prior to startingthe process of installing the intermediate fluid tight barrier 26,whereupon the intermediate fluid tight barrier 26 is installed at leastpartly up to a level prior to starting the process of reinforcing andconcreting the outer structurally supporting wall element 25.

The intermediate fluid tight barrier 26 may according to an embodimentbe formed of thin steel plates in the form of long sheets, delivered onspools. Said sheets are wound in a helical pattern around the exteriorof the inner structurally supporting wall element, adjacent edges of thesheets being welded together to form a tight barrier. The start of thewounding and welding process of the steel sheets may start whenconcreting of the inner supporting wall elements has reached a certainheight. Since it is expected that the welding process will requirelonger time that the slipforming process, it is convenient to postponethe start of slipforming or jumpforming of the outer structuralsupporting wall element until the welding process of the steel sheetsmore or less is completed. It should be appreciated that any stop insuch concreting process should be avoided, since such stop would requirea stop-joint.

According to the embodiments above the structurally supporting elementsof the inner wall is made of reinforced concrete. It should beappreciated, however, that that said portions may be made of a differentmaterial, e.g. in the form of a load supporting wooden structure.

Further it should be noted that the tank may have a different crosssectional shape than the circular shape shown and described inconnection with the drawings.

In case the stored fluid is not cryogenic, an outer tank 16 may not berequired. The tank may also have other geometrical shapes than thecylindrical shape.

Concrete as referred to in this description, may comprise reinforced(conventional non-prestressed) concrete, prestressed and/orposttensioned concrete. Also multi-axially prestressed concrete isincluded in this definition.

In the disclosed embodiment a cylindrical tank for storage of cryogenicfluid is shown. It should be appreciated, however, that the tank may beused for storage of other types of fluids, such as environmentallydetrimental fluids to be prevented from escaping to the environment,fluids exposed to pressure and/or fluids subjected to high temperatures.

It should further be noted that the invention is not limited to tankshaving a cylindrical shape. The tank may as such have any suitableshape.

Further, the tank may not necessarily only be used for storage offluids. A tank according to the present invention may also be used as aroom for implementing processes and/or carrying out reactions.

The joint between the vertical part of the fluid tight wall element andthe corresponding base plate may have any suitable shape preventingformation of cracks or rupture in the joint.

The fluid tight wall element 26 may according to the describedembodiment be made of Ni-steel or an alloy of several metals. It shouldbe noted, however, that such material may be of any suitable type. It isof importance, however, that that the choice of material is such thatthe material is both ductile and fluid tight and made of a materialwhich may withstand the fluid to be stored in the tank.

In the disclosed embodiment the tank is made of two concentricallyarranged separate tanks. It should be noted that the invention is notlimited to two concentric tanks, but may just as much be formed as asingle tank. The need for insulation depends on the intended use and thetemperature of the fluid to be stored and/or the ambient temperature.

The embodiment shows a large tank. Also smaller volumes, e.g. down to 30m³ may be suited.

Further, the embodiment discloses a tank having an inner and outer wallelement 24, 25 made of concrete. It should be noted that at least one ofsaid two wall elements may be formed by a different material, such ase.g. wood.

Reference Numbering List

-   10 Free-standing tank-   11 Inner fluid tight tank-   12 Base plate-   13 Foundation for the inner fluid tight tank-   14 Vertical tank wall-   15 Upper top-   16 Outer tank-   17 Base plate in outer tank-   18 Cylindrical wall in outer tank-   19 Dome shaped calotte-   20 Insulation-   21 Ring shaped base for support of the inner tank wall-   22 Wooden girders form the foundation for the inner tank-   23 Fluid tight barrier on the base plate of the inner tank-   24 Inner structural supporting wall element of the inner tank wall-   25 Outer structural supporting wall element of the inner tank wall-   26 Intermediate fluid tight barrier in the inner tank wall-   27 Steel plate arranged at the lower end of the inner tank wall-   28 Lower, inner, vertical, ring shaped steel plate-   29 Lower, outer, vertical. Ring shaped steel plate-   30 Expansion joint-   31 Anchorage means-   32 Fluid tight, continuous welded seem

1. Tank for storing cryogenic fluids, comprising a tank (11) having abase plate (12), a vertical wall (14) and preferably an upper top (15),the tank (11) being provided with a fluid tight barrier (26) preventingthe stored fluids from escaping out of the tank (11), the fluid tightbarrier (26) preferably being formed of thin, joined metal plates,characterized in that the vertical wall (14) comprises an innerstructurally supporting wall element (24, an outer structurallysupporting wall element (25) and that the fluid tight barrier (26) isarranged between the inner (24) and the outer (25) structurallysupporting wall elements, the structurally supporting wall elements(24,25) and the intermediate fluid tight barrier (26) together forming acompact, structurally integrated and fluid tight wall (14).
 2. Tankaccording to claim 1, wherein the inner structurally supporting wallelement (24) is formed by multi-axially prestressed concrete.
 3. Tankaccording to claim 1, wherein the outer structurally supporting wallelement (25) is formed by multi-axially prestressed concrete.
 4. Tankaccording to claim 1, wherein the intermediate fluid tight barrier (26)is made of a ductile material, such as Ni-steel.
 5. Tank according toclaim 1, wherein the intermediate fluid tight barrier (26) is made ofjoined metal plates.
 6. Tank according to claim 5, wherein the edges ofthe metal plates are bent upwards and folded.
 7. Tank according to claim5, wherein the edges of the metal plates are welded together.
 8. Tankaccording to claim 9, wherein the edges of the metal plates overlap eachother partly and are glued together, or pressed together to form a tightmembrane.
 9. Tank according to claim 1, where the tank (11) is providedwith a fluid tight base plate (23) formed by metal, the base plate (23)resting movable on a support (21, 22) and where the vertical wall (14)is made of concrete, characterized in that the vertical wall element(14) at its lower end is terminated by means of a horizontal metal plate(27) and an inner (29) and an outer (28) vertical steel plate extendingalong the inner and outer circumference of the vertical wall (14), thevertical steel plates (28, 29) being welded to the horizontal base plate(27).
 10. Tank according to claim 9, wherein the horizontal (27) and thevertical plates (28,29) form an integrated unit together with the lowerpart of the vertical concrete wall (14).
 11. Tank according to claim 9,wherein the edges of the metal plates overlap each other partly and areglued together, or pressed together to form a tight membrane, andwherein the lower end of the membrane (26) is welded to the horizontalsteel plate (27), forming a tight joint between the horizontal (23) andthe vertical (26) fluid tight barrier.
 12. Tank according to claim 1,wherein the inner structural supporting wall element (24) is formed bywood.
 13. Tank according to claim 1, wherein the outer structuralsupporting wall element (25) is made of wood.
 14. Tank according toclaim 1, wherein the intermediate fluid tight barrier (26) is formed bysheets of plastic materials, welded together along their edges. 15.Method for constructing a fluid tight tank (11) for storage of fluids,comprising a base portion (12), a vertical wall part (14) of concreteand preferably an upper top (15), the base portion (12) beingconstructed first whereupon the vertical wall part (14) is constructed,preferably by means of slipforming or jumpforming, characterized in thatthe vertical wall (14), comprising an inner structurally supporting wallelement (24), an outer structurally supporting wall element (25) and anintermediate fluid tight barrier (26), together forming a compactstructural supporting fluid tight wall element (14), is reinforced andconcreted at least partly, whereupon the fluid tight barrier (26) isarranged on the exterior of the concreted inner structurally supportingwall element (24) whereupon the outer structurally supporting wallstructure (25) is reinforced and concreted.
 16. Method according toclaim 15, wherein the lower part of the wall (14) is erected on a base,said lower part (14) comprising a base plate (27) of steel, an inner(29) and outer (28) steel plate extending along the inner and outercircumference of the lower part of the wall (14) and further is weldedto the horizontal base plate (27) and where the lower end of the fluidtight membrane (26) in the form of steel plates also is welded to thehorizontal base plate (27), whereupon this portion of the wall isreinforced and concreted.
 17. Method according to claim 16, wherein theinner structurally supporting wall element (24) is erected at leastpartly up to a level prior to starting the process of installing theintermediate fluid tight barrier (26).
 18. Method according to claim 17,wherein the intermediate fluid tight barrier (26) is installed at leastto a certain height before starting the process of reinforcing andconcreting the outer structurally supporting wall (25).